Electromagnetic sound reproducer



Nov. 3, 1931. B. F. MIESSNER ELECTROMAGNETIC SOUND REPRODUCER Filed Aug.. 24, 1929 .i coil excitedwllh 'i Patented Nov. 3,y 11931l i Baumann. r. M'Inssnnnonsnonr nime, :NEW JEitsm'; 'AssiGNon *ro MIESSNER Iiil` v vENrIoNsiNomor Snom; H1LLs, NnW Jansma, A Ycomona'rion or NEW JERSEYv i y y Thel Apresent l invention l,'ifevilatesl,to el'ectroel- `magnetic soundireproducersg and more Apar-V ticularly-` tothoserepl-oducers includingproe c Vision Ik'for Vvmai'ntainingjftherein an intense i magnetic'iield. -f

reproducen in which an intense magnetic iieldy is maintained for interaction with a 'dynamic the soundrepresentmg cnrrents.

' an .Object 0f theinvenueaisfthe prevista of an arrangement whereby the* iield produc ing Vcoil ofv'suchia reproducer caribe excited ;;With a 'uni,-directional'- :pulsating current without disturbing effects onthe dynamic' coil',- andzn particularexcitedrwth incompletelylglteredrectified 1alternatifigcurrent, f y as ishfad in the -novv 4usual practiceof'ener-E 2@ gizing the three-elect'rr'bde vacuum' .tubes/fof t amplifyingsystems-:from commercial 'alternating current fsourcesgf" 1 f 1 u In Ythe usual-mode of construction? of electro'dynamic V' reproducers 1 as*v 'so-called loud 2,5 Yspeakers for Y radio broadcast yreceivers and electrical phonographs 'the giield coil yis 'made' Vof such electrical dimensions thatlits' induci-A tivef'impedancefis ofsnitable valueas to be Y Y .o i. Well adapted to function asthe high inductive 3"' impedaneena filter system associated*withV an alternating current rectifier for Asiufrplying the. plate and grigi energyufor amplifier tubesg Such use eliminates: the'fnsualefchoke -eoilf or onecoil if two 'ormorea'reemployed, o n 3J" auch citer Systeme-thereby Saving Weight,

space -and costv of material; However, the in# completely filtered current at the point in la iiltersystem Where the field coil-mustbe used sulting u p u sirably intense,

In myrapplication Serial Number 3445941,

filed March 7, 192.9, of which this application,-V

i's a continuation.` l'party) Qdis'closecl several forms of dynamic speakersl designed .for op? l eration `under predeterfmined conditions rvvith l 59lm means for neutralizing hum eifects when -ianncamorra'Griii'ri sonni) miritonuom Y limitacin-med .igstfza 1929. serieu No.: 388,131-

the coil thereof was yexcited a source of fluctuating vuni-directional current.y n ,f

v I have found that Whenv such a speaker yvvas 'operated under conditions very abnormal to. the y.conditions for which it was 'designed slightly audible hum developed therein. yIt istherefore; the purpose of this invention to Yprovide an electrodynamic speaker, ythe humneutralization effects within the speaker being variable to adapt the same to Widely vary-l ing conditions ,ofuse and field coil excita'- t'Ol.' y v y i t -My invention will be readily understood Vfrom the following description in connection with the 'accompanying drawings in Vwhich 'Fig'. 1 shows m'across sectional view the usual Vform kof,construction of so-called dy-v namic speakersr arranged to include` features of'my present inyentiomand 'Fig'.Z diagrammatically illustrates suitable electrical connections for taking advantage of the featuresof'Fig. 1.

@Referringnto Fig. l, av magnetic circuit ofthe :usual form of electrodynamic reprosuitable ,series of screws 9. A central corey 2 of softiron or other suitable magnetic mavterialtis bolted to the base of the cylindrical element- `l by abolt das shown, the core 2 extending through a circular opening in the yfrontdisc 4 as shown, .the opening in the disc 4 being ofl slightly. larger diameter than the diameter ofthecore 2 in order to accommodatej'a coil 6 'secured to a cylindrical projection?" ,of va conical sound producing element y t -A coil-5,-u'sually comprisingy many turns of iin'eyvire, encircles the 'core 2, and is arranged With'input terminals 13 and 14 through ,which theield producing` orenergizing current is supplied. This-fooilI.have Wound upon a spool @,theboreof which preferably/'snugly fits the core Q With only suiiicient clearance'to" b@ movcdvtherealong when pressure is exert- Y eaupoa the con. Amandine con 5 i have provided a clamping ring b, having a pressure memberc extending through an apere Vture d in the casing 1. '..Upon the'l casing 1 adjacent the aperture Z'I have provided two lugs 6,6 provided with threaded adjustment screwsV f, f', the axes of which are parallel-cto Y f the aXis of ther'coil 5 andthe pressure tips of which engage the memberc. y vIt is to be un-V V derstoodthat other'means may ibe provided Y core 2 kwithout departing'wironi-thespirit of A rent produces amagncticliux whichfin ina-V for adjusting the coil 5 longitudinally oi" the my invention, the particular structure shown being merely by Vwayl of illustration; lc i,

With the arrangement shown, the energizing ofthe coil 5" with a V'uni-directional' curjorpart takesa path through the -core 2,- the gap between the end ofthe coref'2 and the f.

surfaceof the opening in the disce, through of the gap being markedN and S toindicate Ymagnetic polaritie's, but these rpolarities ican bereversed from( thoseindicated Vwithout a'ltering theimode ofoperation. The coil is so mounted on the cylindrical'entension Y. in

the gap as to be movable therein, andprefenably without interfering-contacts with the' gap portions,l so that'whenfsound ,represent ing currents are applied to this' coil through vthe Vterminals l5 and-16,gthere is a' motion producing Vreaction set up between the coil j and the intense magnetic field of thegap, re-

sulting in `sound reproducing finition being impartedl to the cone? orotlier associated sound reproducing element.V The" usual constructionv of electrodynamic reprodu'cer endeavors to make the air gap as short as the structure of the coil Gfand its mounting on the cylindrical element 7 will permit while v leaving suiicient clearance' to prevent fric'- tional contacts, this in order thatlthe iuXin the gap may be maintained afs intense-as pos,- sible for a givenY strueture'of magnetifc'system `and eld producing coilQ' If the kcoil 5 ijs, energized' from ra source,`

, such as rectified and filtereda'lternating cur.- rent having av pulsatingcomponent,V obvieus-y ly the refsultingflux througlfithe gapwillfloeY oi VVunidirectional pulsating character,V and will react with the'coil 6, with-or vwithout the Asignal representing Vcurrent How, 'to produce mfotion'of the'cone 7 that will'cause'a huml characteristic' of the' 'pi'ilsationsfin the held XCtng current, any kryu ii'desirable feature in soundv reproducing 'devices in general, particularly those used ,for entertainment purposes such as phonograp'hic ,reprodu ction orY 1' ""'Lnat enc-se potentials {aiy'dii'i'ei'entiaily with'v radio vbroadcast reception:v

Y such afsystein is to be subjected. f

Because of convenience, the distaste of the public for batteries and the characteristics of the electrical energyrequired, it is'alinost compulsory to employ energy derived from commercial alternatingcurrent sources for energizing the field coil of current designs of electro-dynamic reproducers. Further, the high inductance availableinthe field coil of commercial lelectrodynamic reproducers makes these coils particularly suitabley as the inductive impedance element of the filterl systemscommonly .usedin connection with ile tering rectiiie'r` alternating current` for ener igizing thevrgplate grid electrodes of threeelectrode vacuum tubeV amplifiers used in radio receivers .and electrical. phonograph reproducers, and such use saves' the expense,

fweightand spacer o additionalcoils for iilter purposes -in yaddition Ato f avoiding the` employmentof a separate sourceofcurrent for energizing the fieldV coili' `In addition,- the users of such devices, apparently 'unconcerned about the electricaldesign thereof',

substitute one speaker ,systemifor Vanother ywithoutv regard to the vconditionsto which For these reasons a ysatisfactory-arrangeL ment forpreventing;theproduction of hum ywhen energizing'th'e field coil with uni-directional v current having widely 'varying 'di-zV y rect4 current and 'iiuctu'ating current come ponente is 'of great importance, andthe fea-rv tures of my present invention ',permit-this hum elimination to bei-accomplished v:ina most effective' degreey by simple adjustments'. In my application hereinbefore referred to I described the action of -a bucking coil yplaced at ypoi-nts within thei magnetic system and foundthat itwas nece'ssaryto govern the magnetic induction in thek bucking coilboth as to intensity andwavefform tobring about most complete neutralization of hum effects.

These principles apply; equally to' the local' tion ofthe bucking coil of. V'my present'invention and Ik havef found that by varying' these effects diii'erentially with the diii'erential variations in fthe y armature coil under widely yvarying conditions of energization ofv the fieldcoiLI can maintain the' satisfactory low hum characteristics goflfthe speaker throughout very" wide vranges ,of operating conditions;r Y. I i Y In Fig. 1,1I'have shown a magnetic circuit employingthe Vfeatures described lwith refer-kence to Fig. 'lot my 'copendingapplication, and have found Vthat by locating thebucling coil 8, o'ta pancake formwfand having terminals 17 and 18, at the base of the core 2, and

Lheld in position closely adjacent the casing l by a` small press-itring 8a, the potentials developed at theterminals 17,18fcan-be varied l vthroughout awiderange of values by the adjustment of the' coil 5 alongjthecorevf. means lof the screws f, Ihave alsoi'olund v'respect tothe varying potentials developed f upon. the terminalsl, 16 of the coil 6.y

Considering lthe '.circuit arrangement of' Fig. 2, ,the core 2 of Fig. 1 isfshoWn Withield coil 5 connected vto be energized by Way of f terminals 13 and' 14:, as from a source 26 of periodically fluctuating uni-directional current. Dynamic coil 6 is shown connectedy to amplifier system.- The coil 6 is connected besupplied with sound representing currents through a transformer 0T connected to, for example, the output terminals 21 and 22 of an inseries With coil 8 through. a potentiometer 2ta'cros's. the terminals 17 and'18, or other suitable means, permitting adjusting ythe magnitudes of the hum bucking current colllected in coil 8 applied to coil 6, a vcontrol Vvequivalent to thefcontrol arrangement described with reference to Fig. 2. of my copending application. Y

n As a practical procedure the coil 8 may be .constructed with more turns than needed for Vneutralizing for anormal positionvof-coil 6, andthe potentiometer used for securing anA v adjustment for taking care of production discrepancies in locationV of coil 6. Or the -po' 1 tentiometer. adjustmentfmay beutilized for correcting for residual hum current coming terminals 1 f from a preceding amplifier.

Vitli a design ofcoil 8 to Veffect neutralization `under a given set of conditions the potentiometer24 may be dispensedwith, the coil 6 being 4directly connected across the of the transformer'OT.k

Wh'en the speaker system is to be operatedV Vunder conditions Widely differing from those .6 and 8 as indicated by the arrow;

j for v'Which it Was originally set, hum neutralization may be again established by varying the position of the'coil 5 relative to the coil VWhile I have-:disclosed my invention withy particularity with respect to specific embodiments thereof, no limitations by reason of such choice for explanatory purposes areV in? tended, the invention being one of broad scope capable of numerous adaptations readily apparent to those skilled in the art.

vHaving fully, described my invention, I

claim; I

' 1. In an electromagnetic sound reproducer,

l the combination of amagnet energized by direct current, Van air gap in the magneticcircuit ofj said magnet, a dynamic coil adapted to be ab said dynamic ycoil and dynamically independenergized with sound representing currents operatively located in said air gap, and means for eliminatingdisturbances in said dynamic coil due to periodicfluctuations of said direct current comprising a second coily coupledv to `.ald magn-etconnected in opposing series with eutftliereof, and means for adjustably differ,-

VVentially apportioiiing the relative intensity of magnetic induction Within said tvvolcoils.y F y 2. In an electromagnetic sound reproducer,

18 throughtlie secondary thefcoinbinati'on of anelectromagnet compris-- ing a core and asolenoid thereon adapted to' ybe y,e'xnrgized with fluctuatingy Aunidirectional current, said lco re constituting; aA magnetic circuityhavingiafgap fitherein, a. dynamic coil; Vadaptedtofbe energized with sound representing currents;operativelylocated in said air: gap, lmeans for eliminating disturbancesy inl-saidl'dynainic coil'duc-to the fluctuationsy of said` uni-directional current comprising a second coil'fconnect'ed vin opposing series with saiddynamic'coil aand dynamically independl ent? thereof, Vandy means for adjustably varyingjfaidJ apportioningy :the relative* induction betweensaid solenoid and each ofy saidV coils.4

:13? I-nan electromagnetic sound reproducer,

the combination of an electromagnet compris--A ing a core andv a; solei'ioid'thereony yadapted to be energized with' iuctuating unidirectional ciirrent,said corecbnstituting a magnetic cir# cuit-liaving a gapjthereiii, a"d'ynamicxcoil adapted to be energized With sound represent- 'ing' currents operativelyl located in said air mea-'ns 'for eliminatingv disturbances in" said; dynamic' rcoil 'due' lto the fluctuations of saidguni-direction al current comprising a sec ond coil connectedinopposing vseries with said dynamicv coiland "dynamically independent" v thereof, y sa'i'dv coils v,being located at opposite ends-vof vsaid -solenoid,'and means for adjustably varying and apportioning the .relative inductionfbetweensaid ysolenoid and each of saidcoils.`l l Y 1 L f 4. In an electromagnetic sound reproducer, the combination 'ofan 'electromagnet comprising a core and a solenoid thereon adaptedV to be energized with fluctuating unidirectional current, said core constituting a magnetic circuit having a gap therein, a dynamic coil adapted to ,be energized Withl sound representing currents operatively located in said air gap, means for eliminating disturbances in said dynamic coil due to the fluctuations of said uni-directional current comprising a secvond coil connected in opposing series with said dynamic coil and dynamically independent thereof, said coils being located at opposite endsof said solenoid and substantially co-aXial therewith, and means-for adjustably varying and apportioning the relative induction between saidsoleiioid andveach of said coils.

'5. In an electromagnetic sound reproducer,

'the combination of a magnetic system having isc ment of said'dynamic coil byvariationfs inthe;- i

flux of said solenoid; i

- .Iny anieleetl:oln'agneticsoundreproducen A y y Y Ythecombination cfa magnetic system having f f 75l a'gap therein, a' solenoid surijounding .a por-Y tion of Said magnetic'-system fonproducinga.y magnetic 'luxacross said' gap a dynamic'coilfv mounted "Within said substantially( co-A V axial vwith said solenoid,v a lsecond coilelec!k 10' tiieally/connected in opposing sei'ies'with said dynamic coil and co-axially'mountedY at one end'of said solenoidat an appreciable distance therefronnand means for varying the'relative. positiony oi saidfsolenoid between said two 157 coils for tlieelfimination of displacemento said vdynamic: 'coil' by" ,variationsv lin y the` Hu); O-i'ls'ald' solenoid# f l e A i' .5 -In anjelectromagnetic translating Ydevicey A including a magnetic eldfhaving a l'luctn'at-- 20 ving component and a movable coil adapted tov bei energized-by Sig'nalfciirrents and linked with flux 'of said'inagnetic field, the combi-` nation of an yauxi'liaryY coil having a uX intei'linkage jWith said 'magnetic field of sub- 25? stantially like harmonicl composition as that in saiduniova'ble coil, connections forV oppos- Y ing the fluctuating energy-=com`p0nents transferred from saidmagnetic field to both of Said l; .y coils, and means for adjustably. differentially 30? apportioningksaid transferredl energy com# ponents. v. Y f y i In Witness Whereoil have hereunto subscribed my lname this 23rd day of Angust,

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